Direct communication between a terminal and a terminal (Device to Device (D2D)) enables direct communication between terminal devices without requiring any intermediate infrastructure. Therefore, the direct communication between terminal devices can use spectrum resources more efficiently, increase a capacity of a cellular network, and reduce overheads of control signaling of a base station.
Although all systems such as wireless fidelity (Wi-Fi), Bluetooth® (BT) and an ad-hoc network (Ad-Hoc) in the prior art may implement D2D communication, a complex maintenance problem of timing occurs. This problem is: Receive timing of a terminal that receives a D2D signal needs to align with uplink timing or downlink timing of a terminal that sends the D2D signal at the peer end. During D2D communication, a terminal maintains not only its transmit timing but also its receive timing, resulting in complex maintenance of timing and high energy consumption of the terminal.